This invention relates generally to shutdown circuits and specifically to a shutdown circuit for a power supply utilizing a pulse width modulators (PWM).
Switch mode power supplies have found rapid acceptance because of their high efficiency and adaptability to changing load current requirements. They are widely used in conjunction with electronic consumer products and computer equipment. Even in large main frame computer installations, where the power may be derived from 240 volt three phrase power lines, pulse width modulated power supplies are utilized for supplying the low voltage, high current requirements of the connected computers from the high input DC voltage developed by the main rectifier system. A drawback of pulse width modulated supplies is that they tend to overheat in the event of significant voltage drops on the input circuit. In most cases, it is preferable to shut down the power supply and the attached equipment, which is sensitive to voltage, in the presence of sustained low input voltages.
The circuit of the invention provides an economical, efficient, low voltage shutdown arrangement for sensing when the input voltage has dropped to a predetermined level for a predetermined time period and for initiating a utilization device for developing a shutdown signal.